It is well known that metal vapors are particularly useful for stimulated emission of certain desired wave lengths. Many metal vapor laser transitions are well known, including copper at 5106 a, lead at 7229 A, and manganese at 5341 A and 12899 A. Of the metal vapors, copper is considered one of the most desirable because of high efficiency, peak power, and optical gain. Presently, metal vapor lasers require very high temperatures (1000.degree.C to 1600.degree.C) to generate sufficient vapor pressure to reach laser threshold conditions. Additionally, the laser pulse in metal vapor lasers is limited in duration by the time required to destroy the population inversion by filling of the lower laser level due to stimulated transitions. That is, if the rate of removal of lower laser level atoms is much slower than the pump rate or laser transition rate, the population of the lower level will build up, destroy the population inversion, and choke off the laser oscillations before the pumping pulse is complete. This self-limiting operation is common to most metal vapor lasers and, consequently, limits the efficiency and output power obtainable therefrom.
Various attempts have been made to overcome the self-terminating action of the metal vapor laser. One approach was to introduce an impurity such as a molecular gas in the belief that it would collisionally de-excite the lower laser level. While this was successful in molecular lasers such as CO.sub.2, it did not prove successful in atomic vapor lasers. Another attempt was to sharpen the leading edge of the pumping pulse so as to increase the pumping rate into the upper level. This proposal was to increase the peak power in the pulse, but not its duration. While the method is generally successful, the amount by which the rise time of high current pulses can be lowered is limited.
Accordingly, it is an object of the present invention to provide a method and means for depopulating the lower laser level while maintaining sufficient population in the ground state to effect resonance trapping of radiation leakage from the upper level to the ground state.